For the operation of an integrated circuit, for example an integrated semiconductor memory circuit, the memory chip is connected to an external supply potential and also an external ground potential. In full-load operation of the memory module, however, voltage dips may repeatedly occur on the supply voltage and the ground voltage. Such voltage dips arise, for example, when current spikes occur on account of commands that are applied to the semiconductor memory. This problem is widespread particularly if the circuit layout of an integrated circuit does not satisfy the high-frequency requirements or the ground lines are highly inductive.
On account of these voltage fluctuations of externally applied voltages, integrated circuits are generally operated with a stabilized voltage internally. Linear regulators have hitherto been used for generating a stabilized voltage, said regulators generating, from an externally applied, non-stabilized supply voltage, a stabilized internal voltage with which the circuit components of the integrated circuit are operated. Among the linear regulators, series regulators have become widely used owing to their simple construction, particularly in integrated form. However, integrated regulators require a certain differential voltage between input and output, apart from a few special types.
Present-day memory generations are specified, in relation to the regulated and stabilized voltages used in the chip, for external supply voltages that are of the order of magnitude of the internal voltages. Thus, in future DDR-DRAM (Double Data Rate Dynamic Random Access Memory) semiconductor memories, for example, the external supply voltage will be 1.8 V+/−0.1 V, but the semiconductor memory module will be operated in a technology-dependent manner with an internal voltage of 1.8 V or 1.5 V, for example. By virtue of the non-existent or very small difference between external voltage and internal voltage, a regulation of the internal voltage by series regulators becomes impossible or inefficient.
However, if the internal voltage of an integrated circuit cannot be kept stable by means of such regulators, the result is that internal voltage networks are operated below their desired voltage. In the case of integrated semiconductor memories, this leads to a serious impairment of the specified time parameters. The specified time parameters of an integrated semiconductor memory include the precharge times, for example, which are necessary in order to precharge bit lines of a memory cell array to a common equalization potential. An impairment of the internal time parameters on account of an under voltage operation can be explained by the fact that transistor chains are generally used for generating the time parameters. If the transistors of a transistor chain are operated below a specific desired value of the supply voltage, this leads to a retardation of their switching behavior and thus to a temporal delay of a procedure generated by the transistors.
Besides the use of linear regulators, the use of charge pumps would also be conceivable for generating a stable internal supply voltage. Such charge pumps are used in integrated circuits if operating voltages lying above the externally applied supply voltage are required for operating circuit components of the integrated circuit. In the case of integrated semiconductor memories, a charge pump is used, for example, for generating the word line voltage, used to turn on the selection transistors of the memory cell array, since control voltages that lie significantly above the externally applied supply voltage are necessary here. The use of an additional charge pump for the stable voltage supply of current-intensive networks on the semiconductor memory chip cannot be realized, however, on account of the specified maximum current consumption.